The present invention relates to the field of remote control devices, and more particularly to transmitters for remote control of apparatus such as vehicle security systems and garage door opening devices.
Remote control of various electronic and electrical devices via transmitters operating at radio frequencies is now common. For example, vehicle security systems and garage door openers are examples of apparatus commonly controlled by radio frequency (RF) transmitters. Many of the controlled apparatus have a variety of features which may be controlled remotely. For example, vehicle security systems may be armed or disarmed remotely, and various additional features such as actuating the vehicle power door locks, remote engine starting, and the like can be controlled by remote control.
It is desirable that the remote control transmitter be small in size, and preferably suitable for hand-held use. In the case of a vehicle security system, the user may carry the unit on a key chain, so that the transmitter unit is preferably quite small. If the controlled apparatus has only one function that may be remotely controlled, or if the transmitter is to be used to control only a single receiver device, then only one code need be transmitted. In that event, only one control switch is required to operate the transmitter. But as the number of functions to be remotely controlled increases, or if the transmitter is to be used to control more than one receiver apparatus, then the transmitter must be capable of transmitting more than one code. To accommodate the increase in the number of available codes, the complexity of the transmitter controls has also increased.
Typically, to control multiple functions or receivers, the transmitter includes means for transmitting multiple channel codes, the receiver apparatus being responsive to one or more of the different received codes to activate a predetermined function associated with the received code. Conventional transmitters have employed separate function switches or buttons, one for each possible channel. To operate, the user simply pushes the appropriate button to send the particular code signal for a desired function. Thus, where two functions or receivers may be controlled remotely by the transmitter, conventional transmitter devices have employed two push button switches, one for each channel. In another known arrangement for selecting and transmitting one of three channel codes, the transmitter is provided with first and second switches. To transmit a first channel code, the first switch is pressed. To transmit a second code, the second switch is pressed. And to transmit a third code, both switches are pressed. In addition to the limitation of the small number of usable channels, the foregoing transmitter apparatus can be inadvertently activated simply by unknowingly actuating a switch, as when the transmitter is being carried in a pocket or a purse. And as the number of functions increases, it becomes impractical to add many switches since it will increase the size, cost and complexity of the transmitter and its controls.
In another known type of transmitter which provides the capability of selecting and transmitting one of nine possible channel codes, the channel is selected by an electromechanical thumbwheel switch. This transmitter is limited in the number of available channels to the number of different thumbwheel positions (nine). Moreover, the thumbwheel position cannot be seen in the dark by the user, who will therefore not be able to tell which channel has been selected unless the switch is viewed in the light. For vehicle security systems, this is a major drawback, since the user often operates the system at night in unlighted areas.
It is therefore an object of this invention to provide an improved multichannel transmitter for remote control of a plurality of functions or different receiver apparatus.
Another object of the invention is to provide a remote control transmitter which provides the capability of user selection of one of many possible channels with a minimum of control switches.
It is another object of this invention to provide a remote control transmitter which cannot be activated inadvertently.
A further object is to provide a remote control transmitter which provides a signal to the user indicative of the channel selected by the user.
Still another object of the invention is to provide a remote control transmitter which provides a signal to the user indicative of the low battery condition.
Other objects of the invention include providing a transmitter having very high security through a security code comprising a large number of bits, at no increase in the number of output pins of the encoding circuitry, the capability of programming the security code electronically rather than by using switches, punch lines or conductive traces which are selectively scratched, and the capability of providing various security code levels in the same type of devices without an increase in production cost.